A disk cartridge is disclosed in the Japanese Patent Application Laid Open No. 2003-109343. This disk cartridge includes a cartridge body incorporating an inner rotor and shutter mechanism. The inner rotor houses an optical disk. The inner rotor rotates inside the cartridge body. When an opening formed in the inner rotor coincides with an opening formed in the cartridge body, the optical disk housed in the inner rotor is exposed to outside.
Note here that an optical disk used as a recording medium in the disk cartridge has information signals recorded at a high density. Dust or like, if any, adhering to the optical disk will make it impossible to record information signals accurately to the optical disk. On this account, to keep the opening from being uncovered while the disk cartridge is not in use, a locking member is provided to keep the inner rotor from rotating. The locking member includes a locking portion provided pivotably inside the cartridge body to be engaged in a concavity formed in the periphery of the inner rotor, and a to-be-operated portion which cancels the engagement of the locking portion in the concavity when the disk cartridge is located into a disk recorder and/or player.
In the locking member, the engagement of the locking portion in the concavity is canceled if the inner rotor is forcibly rotated while the disk cartridge is not in use. If the locking portion of the locking member is disengaged from the concavity in the inner rotor, inner rotor is rotated and thus the optical disk is exposed to outside, dust or the like will possibly adhere to he surface of the optical disk, thereby making it impossible to positively write or read information signals to or from the optical disk.